It has been general practice to wear on the head a head-mounted display connected to a game machine and to play games by operating typically a controller while watching a screen displayed on the head-mounted display. With an ordinary stationary display connected to the game machine, the user's field of view extends outside the display screen. This tends to prevent the user from concentrating on the display screen or from experiencing an immersive sense of the game. By contrast, wearing the head-mounted display allows the user to watch nothing but the image displayed on the screen of the head-mounted display. This enhances the sense of immersion in a visual world and boosts the entertaining nature of the game being played.